1. Field of the Invention
This invention relates to refractory insulation for support elements in heat treating furnaces and, more particularly, to means for securing insulation on the support elements.
2. Description of the Prior Art
Heat treating furnaces, for example walking beam furnaces or roller hearth furnaces, typically employ support elements, such as water cooled pipes having skid rails or the like, for supporting a work piece as it is conveyed through the furnace. To minimize heat loss from the furnace into the cooling water, the pipes are provided with jackets of refractory insulation. The jackets are typically formed in semi-cylindrical pre-cast segments, or similar configurations, which are joined to one another to encircle the support elements. To facilitate interlocking the segments to one another, metallic straps are integrally cast with the refractory material, and the strap ends have means for interlocking one to another, as shown in U.S. Pat. No. 3,781,167.
Problems heretofore experienced with refractory insulation include the following: The useful life of refractory insulation jackets is relatively short, so the heat treating furnace must regularly be shut down for work personnel to enter the furnace and repair or replace insulation. The more complicated the attachment, the more time required to loosen old insulation and install replacements. Additionally, the shocks and stresses incident to movement of the work piece through the furnace causes refractory insulation segments which have no locking mechanism to work free from one another. Loose insulation thus may fall to the furnace floor, leaving the water cooled pipes directly exposed to the furnace atmosphere.
U.S. Pat. No. 3,781,167 discloses no-weld refractory coverings for water cooled pipes wherein metallic straps are anchored and pre-cast into semi-cylindrical insulation segments. The straps have opposing slots on their ends which are intermeshed to hold corresponding insulation segments to one another around a water cooled pipe. A second embodiment of the straps includes a first strap end having peripheral slots and a second strap end having mating tabs which are received in the slots to interlock opposing straps. The first embodiment of the straps is subject to loosening and fall-off of individual segments since there is no means for positively locking the opposing slots to one another. The second embodiment appears to require manufacturing within very low tolerances. If the tabs are even slightly larger than the opposing slots, the opposing strap ends will not interlock properly, thus unduly increasing installation time and labor. It also appears that the second embodiment would be difficult to disengage for repair or replacement.
U.S. Pat. No. 4,182,609 discloses a protective refractory member having clips and wire mesh pre-cast within the refractory member halves. The clips engage openings in the wire mesh to secure opposing halves to one another. There is no mechanism for positively interlocking the clips in the mesh. Opposing halves may thus work free from one another and fall from the support element.
A third and similar means for interengaging refractory segments is shown in U.S. Pat. No. 4,429,721. Again, this arrangement has no locking mechanism.
Finally, it has become common in the art to tack weld opposing strap ends to one another to protect against working free. Alternatively, others in the art have welded lock rods at appropriate locations on the strap ends, which are bent on-site by installment personnel, to capture one strap end on another. Each of these alternatives requires an additional installation and removal step, which is undesirable from the standpoint of labor and down time.
Therefore, it is an object of the present invention to provide a mechanism for interlocking refractory members which automatically prevents opposing members from working free due to normal stresses, strains and vibrations within the heating furnace. It is also an object to simplify installation and retrofit of refractory insulation to minimize the expense and labor associated with heating furnace down time. It is a further object to provide a device for locking refractory insulation members which requires no welding, or similar added step, at the point of installation, and which is also relatively easy to unlock for repair or replacement.